Confining the equilibrium hard-sphere fluid changes both its excess entropy (relative to ideal gas) and its self-diffusivity. Interestingly, the relationship between these two quantities remains virtually unaltered [1]. Since classical density functional theories for inhomogeneous fluids can be used to accurately estimate how confinement impacts excess entropy, the existence of a “master curve” for excess entropy and self-diffusivity allows one to use thermodynamic information to predict how confinement impacts single-particle dynamics [1]. Given this information, it is natural to ask, “Do similar observations pertaining to the thermodynamics and dynamics of confined fluids apply more generally to pure fluids of attractive particles? Do they apply for mixtures?“

Here, we present results from extensive grand-canonical transition-matrix Monte Carlo and molecular dynamics simulations which elucidate the connections between self-diffusivity, density, and excess entropy for two of the most widely used model “simple” attractive liquids, the equilibrium monatomic Lennard-Jones and square-well fluids [2], as well as for binary hard-sphere mixtures, in confined environments. We show that the implications of confinement for the self-diffusivity for all of these model fluids, over a broad range of equilibrium conditions, can be predicted accurately based on knowledge of the bulk fluid behavior and the excess entropy of the confined fluid.

[1] J. Mittal, J. R. Errington, and T. M. Truskett, Phys. Rev. Lett. 96, 177804 (2006).

[2] J. Mittal, J. R. Errington, and T. M. Truskett, J. Phys. Chem. B (under review).